When a sequence of images is successively captured by a sensor as in particular in the case of a video, conventionally an estimation of inter-image global motion is carried out. This estimation of motion aims to determine the global motion affecting the image sequence between two successive images. It can correspond to the determination of the motion of the line of sight of the sensor used.
Such a global motion estimation allows in particular a stabilization of images to be implemented, or also denoising of images, or installing a super-resolution mechanism.
However, this type of mechanism can be substantially disturbed when the captured scene corresponds to one or more large objects that are mobile during the course of the sequence of captured images or also when the sequence of captured images has low contrast. Thus, in the latter case in particular, it is possible that the global motion estimation is in the end incorrect.
Some image processing systems rely on a sequential implementation of a global motion estimation and a dense motion estimation or also ‘local motion estimation’.
A dense motion estimation consists of an estimation of motion at each point of the images of the captured sequence between two successive images. When a global motion estimation followed by a dense motion estimation are carried out sequentially, the latter estimation can be carried out on images that are compensated based on the preceding global motion estimation.
Then, the dense motion estimation makes it possible to calculate a residual motion at any point of an image. To this end, it is possible to rely on the fact that mobile objects have trajectories that vary slowly relative to the speed of acquisition of the images. This concatenation of the global motion estimation and the dense motion estimation can provide a high-performance estimation of motion in the case where the global motion estimation is itself reliable.
Conversely, when the global motion estimation is unreliable, motion estimation obtained in the end at the output of the subsequent dense motion estimation cannot be reliable and high-performance.
The invention aims to improve the situation.